1. Technical Field
This invention relates generally to ultrasonic welding tools, and more particularly to the materials and process used to make such tools.
2. Related Art
Ultrasonic welding is a technique used to join parts or workpieces comprising hard and soft plastics, and metals. In ultrasonic welding of thermoplastics, vibratory energy is applied to the plastic workpieces by an ultrasonic welding tool, causing local melting of the plastic. The vibrations are transferred through the plastic workpieces to the joint to be welded. The tool can remain in a single location on one of the workpieccs to be welded and the ultrasonic energy will travel through the plastic workpieces and weld the entire joint.
Ultrasonic welding can also be used to join metals, preferably dissimilar metals. The vibrations travel through the metal workpieces and the welding occurs due to local motion of the metal material and high-pressure dispersion of surface oxides. The high frequency vibrations cause some heating of the metals, but not enough to melt the metals.
Ultrasonic welding can also be used to enhance the soldering process. Ultrasonic soldering includes introducing the high frequency vibrations into molten solder and introducing a cavitation action at the welding tip, which disrupts and disperses the surface oxides. The disruption of the surface oxides permits the solder to wet the metal workpiece so that a solidified solder is formed behind the tool.
Ultrasonic welding is a preferred method of joining small workpieces which are too delicate for traditional welding techniques, such as wires and delicate circuits. Ultrasonic welding is widely used in the packaging industry, especially for foods and medical supplies. Further, ultrasonic welding is quicker than traditional welding systems, and it does not require a ventilation system to remove heat or exhaust, which are often needed in other welding systems.
An ultrasonic welding system typically includes a power supply delivering a high power AC signal to a converter, which converts the AC signal into a mechanical vibration. As indicated above, the ultrasonic welding tool, also known as a sonotrode or horn, applies the high frequency vibrations to the workpieces to be welded. A booster can be used to modify the amplitude of the vibration. The converter, booster, and tool are specifically tuned to resonate at the same ultrasonic frequency, which typically ranges from 15 kHz to 70 kHz. The workpieces to be welded are held in a press under pressure to prevent the workpieces from being forced apart as the tool applies the mechanical vibrations.
Although ultrasonic welding has numerous advantages, the technique has limited use due inadequacies of the tool. Existing ultrasonic welding tools are typically wrought or cast from a metal alloy. Upon forming the basic structure of the tool, it must be machined to achieve desired features and shape, which is costly and complex. The manufacturing and finishing processes limit the selection of material available for use as an ultrasonic welding tool. Further, the available materials are not compatible with the workpieces to be joined, thus further limiting the use of ultrasonic welding as a method of welding workpieces.